I would like to know more about the adverse effects of ketamine. How much is too much? How often is too often?
Ketamine should not be used combinated with other depressants (alcohol, GHB, benzos…). Changes in body perception and anaesthetic effect can lead to problems when someone is under its effects. If you get burn (by a cigarrette, for example) or suffer some wound under K effects it is possible that you don´t notice it. Loss of motor coordination is a common adverse effect depending on dosage.
There has been some concern about ketamine and neurotoxicity but there is no evidence of this in humans and probably, it is not a problem. “Ketamine bladder” is the most important problem related to its use. Frequent ketamine use can injure the bladder, causing ulcers (wounds) and fibrosis (stiffening of the bladder walls and shrinkage). Patients refer urinary frequency, urgency, pressure, pain, incontinence and/or bleeding from the bladder. Treatments are not very effective. In general, this problem appears in intensive, dependent persons who take several grams a day/week, although there are exceptions to this rule.
Dependence potential of ketamine is another important problem. It is clear that some people are unable to control their ketamine use, and develop a desadaptative pattern of use where control is lost (similar to cocaine or heroin).
It is very difficult to decide how much is too much and how often is too often. If we make this question for alcohol (as an example of a common drug) we would have very different answers. In general, ocassional use in recreative contexts of moderate dosages is much less risky than daily or even weekly use. Risks increase with frequency and dosage but these are not the unique factors. As a general rule, regular use of drugs increases risks of problems. Less is more.
More reliable information on K effects and problems: